German authorities are investigating 60 asylum seekers suspected of possible links to terrorist organizations, including Islamic State, the Federal Criminal Police Office BKA said on July 25.

"Considering the ongoing migration movement into Germany, we have to assume that there are active or former members, supporters and sympathizers of terrorist organizations and Islamist war criminals among the refugees," the BKA said in a statement.

The statement said police did not currently have any concrete indications of attack plans.

Police have received a total of 410 tip-offs from local authorities in Germany's 16 federal states on possible terrorists among refugees, the statement said.

Meanwhile, Interior Minister Thomas de Maiziere was quoted by German media as saying it would be wrong to put all refugees under general suspicion, "even if there are investigations in individual cases."

De Maiziere called for Germany's borders to be better protected without preventing refugees from coming to the country by legal and safe means — "in reasonable numbers."

Germany witnessed four armed attacks on members of the public in less than a week, three of them carried out by asylum seekers.

More than a million asylum seekers have entered Germany over the past year, many fleeing conflicts in Afghanistan, Syria, and Iraq.